ועתה לך ואנכי אהיה עם פיך והוריתיך אשר תדבר ... (ד-יב)
MASHAL: In the city of Vilna, the position of cantor became available, and a man by the name of Rabbi Moshe Rivkes was a leading candidate for the spot. Many favored his cause, claiming that he was the perfect person to lead their congregation in prayer, while some were against his candidacy on the grounds that he did not have such a phenomenal voice. The two parties brought the case to the great Rav, R’ Shabsi HaKohen zt”l (known by the acronym “Shach”), and after hearing the arguments, he sided with those who favored Rabbi Rivkes.
The opponents of Rabbi Rivkes asked him, “Is it not a fact that one of the qualities required by Torah law is that a chazzan should have a beautiful voice?”
“Yes,” answered the Shach, “there are indeed a number of important qualifications required in halacha; he should be over the age of 30, a man of education, a G-d-fearing Jew of pleasing personality, and one with a good voice. As to Rabbi Rivkes, you all concede that he is of age, a first-class scholar, a G-d-fearing individual, and has a pleasant personality. All you differ about is the quality of his voice. Why bicker over only one tiny little detail like that?”
NIMSHAL: Moshe Rabbeinu humbly told Hashem he was not fit to be the leader of Klal Yisroel because he had a deficiency: he could not articulate properly. To this end, Hashem told him, “Since we both agree on your unsurpassed qualifications and your only argument left is your unqualified voice, why must we bicker over a small detail like that? You go and I will be with your mouth.” When Moshe refused even that, Hashem became upset and punished him by giving Aharon the position of Kohen Gadol, which was originally meant for Moshe.